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How to build an underground storm shelter tornado bunker

03-21-2014, 10:22 PM

**I'm willing to pass on any information that I've learned/compiled. I can't include step by step, as it would take up hundreds of pages. If someone else is wanting to take this on, I'll help how I can.

Thought I would post this because before I started mine I found little to no information out there. I've been researching/planning this project for a long time now, but finally started on it a little over a month ago. First off, I decided to go with a steel shelter. Concrete will crack over time, especially with moisture and temperature fluctuations. Cracks mean leaks. Fiberglass also cracks- where I live small earthquakes aren't that uncommon, so I decided steel because it will flex. The only downside to this that it will be susceptible to rust... but with coal tar epoxy coatings and cathodic anode protection, this thing will outlive me many times over. I'll explain that when I get to it in the posts.

I started out by purchasing 3/16ths plate and lots of 5lbs/foot c-channel (12 20 foot sticks). The material bill was right at $1800. This was right at 4000 pounds of metal. If you notice, commercially built shelters are all 10, 12, or some cheap ones even 14 gauge sheet metal. 3/16ths is almost twice the thickness of 10 gauge. I decided against shipping containers as they are 14 gauge- you can email me for more details if you want the argument of why they're not the best choice for underground shelters. Mine will be buried at least 1.5 foot underground. I will also have power and Ethernet feeds to the shelter. The final shelter will be 6 foot 1 inch tall inside, 10 feet long inside, and 6 feet wide inside.

Materials purchased:

Floor Bracing Complete: The floor is actually 12 foot long. This will give me a footprint bigger than the shelter itself to allow me the ability to use concrete to keep the structure from "floating".

I used a hydraulic engine hoist to maneuver some of the sides into place, and borrowed my neighbors front end loader for part of the work. I don't have access to a forklift, or this job would have been way easier!! I just cut small 1" pieces of c-channel to use as hooks, and welded it on my pieces. This made it easy to pick it up using a chain.

Second Wall:

Welding Second Wall in Place: Note the upright folding table- it was windy and this blocked the wind from my shielding gas.

I should've mentioned prior, I am making a welded seam along the outside and inside edges of this project. After I had my skeleton pieces in place for support, I welded along the bottom seams. After the seam was finished I welded the middle support. I then removed (cutting wheel on grinder) the supports that were holding the sides to continue the seam. Ultimately I welded the supports back in place after I had completely welded the seam.

I put a few structural braces along the top inside for the top to rest on , so that the roof could rest safely while I continued the outer skeleton.

As mentioned earlier, I used 1" drops of C-Channel to make the lifting hooks. I also used this approach previously to lift the walls.

Had to borrow my neighbor, and a few friends to get the roof in place. After raising it, we had to maneuver it and eventually slide it on top of the structural braces that I had previously welded across the top inside.

I'll be buying some beer and smoking some BBQ on that reverse flow (prior post) to thank these guys!.

After the roof was in place, I had a gap on one side. I improvised with pipe clamps to pull this in the best I could, and went to work with the wire. Got it filled in with a few passes.

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I was able to bead the entire edges of the outside of the structure, and later finished the same on the inside. This will give me 2x the water protection just in case.

As I went along, I continued my exoskeleton to add strength to this shelter. You'll notice the c-channel is not spaced completely even. This is to compensate because of the overhead supports in place under the roof. This will distribute the topsoil weight more evenly over the frame of the structure.

Using the C-Channel hook method, another piece was fit in to place on the end of the structure. I used pipe clamps to keep it held in to place while I began my welding. This piece alone weighs over 400 pounds, so I it was a task getting it fit in to place. The top will be trimmed off here shortly, and the drop will be used for the entry hatch.

To be continued.......

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In your original post, I am getting an invalid attachment specified, but I could see the rest.
Are you going to drag this to it's finally resting place or what?
I think the C channel would give more structural rigidity if it were turned the other way with the flanges to the sheet metal. Don't forget to give some consideration on ventilation for this before installing it. You may want to breathe some when y'all are in it. I think it would be a good idea to have the entrance door swing inward rather than outward. A tornado cold drop something across the doorway blocking you from opening it after the storm has passed. Then you would be dependent on someone clearing the doorway from the outside before you could get out.

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Thanks for all the advice. I'll see if I can fix the original attachments this evening. I'll be using a large excavator to dig the hole and lift and move the structure. A large backhoe has the lift, but where we live it's really sandy soil. An excavator gives me more lift capacity, and a longer reach so we don't sink an implement into the hole. The shelter will have powered ventilation with an air input and output. As for the door, I originally wanted an inward swinging one, but keeping out water I thought would be a challenge, and it would interfere with my stairs. I ultimately decided to implement a bottle Jack into the door so that I can lift the door if necessary.

If you have any ideas on a door that would open inward and work with those challenges- that would be better IMO.

About to get some time under the hood!

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Thanks for all the advice. As for the door, I originally wanted an inward swinging one, but keeping out water I thought would be a challenge, and it would interfere with my stairs. I ultimately decided to implement a bottle Jack into the door so that I can lift the door if necessary.

If you have any ideas on a door that would open inward and work with those challenges- that would be better IMO.

About to get some time under the hood!

If you installed this with a slight slope toward the door that would help, as would GOOD weather stripping around the door. Make a small well area just in front o the door and install an electric sump pump with a float switch would handle any accumulated ran water. I would be more concerned with being trapped inside by debris against the door than water intrusion. You would just be there until someone outside thought to come looking for you. How long are you willing to wait for out side help when you could be out trying to help others instead?

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While I don't know what to suggest, Hurricane Irene in 2012 taught me to think outside the box. VT doesn't get storms. The statement isn't quite true. When everyone around me was prepping for a hurricane, I checked for trees that might be weak, knocked down any close enough to hit a building. The mountain brook is 200 yards away, and 50 feet in elevation below, I wasn't worried.

Hours before the full brunt of storm my neighbor called, the dry brook had water. Something that happened twice in the twentieth century. I walked out and watched. In five minutes water rose from a trickle to a raging river 18 feet deep, and 300 feet wide. Three hours later the water subsided. Though we don't appear on the flood maps, we were inundated. Chipmunk population hasn't returned.

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Except that a solid metal box buried in the ground probably makes an excellent faraday cage...

At the very least, make a smaller trap door in the main door that can open inwards and out of which you can poke the phone ... Or shout for help... Or just check that everything outside is ok

Frank

Another thing to consider is after a storm like this, any local cell towers may be down too. You can't always rely on total cell phone coverage after a major storm like a tornado. Having a landline phone line installed would be a better option, but still not fail safe. I would still do a inward swinging door.

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I came across your post too late but how about a second door or means of escape?

Groundhogs always have at least 2 exits for their tunnels.

On a similar note, in 1970 my high school classmate's parents moved 20 miles away.
He still attended my school so all was not lost.
One day after the move, he invited us to come out and visit.
New house had a fallout shelter in the backyard built by the previous owner.

Win-win situation - my friend and his band buddies used it for playing
as loud as the wanted and the parents loved it's soundproof qualities.